To maintain their sharpness, cutters on cutting chains must be ground after periods of use and whenever the cutting chain encounters rocks, contaminated wood, or other anomalous material. The cutters are sharpened on the chain by placing the chain in a bench grinder 20.
FIG. 2 shows a typical cutter 36 with reference numbers identifying critical features which will be described more fully below including top plate length 42 and top plate angle 34.
A depiction of a common bench grinder 20 is shown in FIG. 1. The common bench winder 20 has three main components: the grinder head 22 containing the grinding wheel 24; the grinder base 26; and the vise 28. The grinder head 22 is attached to the grinder base 26 at a top back pivoting binge 30. The vertical angle of the grinding wheel 24 can be adjusted between 90° and 45° to adjust the cutler top plate sharpness angle 32 (See FIG. 2). The vise 28 can be angularly positioned around an axis that is substantially normal to the horizontal plane of the grinder base 26 between angles of about 40° and −40° to adjust the top plate angle 34 (See FIG. 2) of the cutter 36. Some grinders are equipped with a tilting portion (not shown) that tilts the cutter 36 to create a sharper angle at the overthrow edge 38 (See FIG. 2) of the cutter 36.
Grinding cutters 36 includes securely clamping the chain 40 between two rails on the vise 28. The cutters 36 alternate on the chain between left-handed and right-handed cutters. One orientation of cutters (e.g., the left-handed cutters) are ground first, with the chain 40 being positioned longitudinally in the vise 28 with the cutter 36 positioned against a cutter stop (not shown).
The grinder 20 must be adjusted for grinding in the following order: 1) the grinder head 20 is angularly adjusted to grind the top plate sharpness angle 32 (see FIG. 2); 2) the vise 28 is angularly adjusted in its base to set the top plate cutting angle 34 (see FIG. 2); 3) the down angle is adjusted by tilting the vise 28; 4) the depth of grinding is adjusted using the depth stop 44 which is set by lowering the grinding wheel 24 down until the grinding wheel 24 touches the gullet 46 (see FIG. 2) of the cutter 36; and, 5) the cutter stop is longitudinally positioned on the vise to adjust the top plate length 42 of the cutter 36.
The same procedure is followed for cutting the opposite hand cutters by rotating the vise 28 to reset the top plate angle 34.
With current grinders on the market it is difficult to achieve the same hook angle 48 and top plate length 42 between the right and left handed cutters on a change. This difficulty is mainly due to the fact that the vise 28 has one side fixed to the vise base and a second side that adjusts in and out for clamping the chain 40 in the vise 28. When the vise 23 is rotated to cut opposite hand cutters, the fixed side of the vise 28 changes relative to the grinding wheel and the operator must then readjust the longitudinal position of the cutter stop on the vise to try and make the top plate lengths 42 the same for both left and right hand cutters. This adjustment also creates a difference in the hook angle 48 between the left and right handed cutters. Differences in top plate lengths 42 between left and right handed cutters 36 beyond 0.020 inches can cause undesirable differences in the hook angle 48 between the left and right handed cutters 36. When the hook angle 48 varies much beyond 4° between the left and right handed cutters 36, the cutting chain 40 will have a tendency to pull from a chain saw one direction or the other when in use.
Additionally, current grinders utilize a stiff torsional spring 50 on the hinge 30 to bias the position of the grinding head 22. To overcome the stiffness of the torsional spring 50, the grinders 20 include a large handle 52. Overcoming the stiffness of the torsional spring 50 can lead to an operator pressing the grinding wheel 24 down too hard and thereby causing the grinding wheel 24 to grind the cutter 36 too deeply, even burning the cutter 36. Also, the torsional spring 50 is difficult to replace when it breaks because it requires disassembly of the grinder head 22 from the grinder base 26.
Embodiments of the invention address these and other disadvantages in current cutting chain grinders.